Structure and Bonding of C₂H₂ on Diamond C(111)−1×1:H:  Infrared Spectroscopy and Exciton Calculations

Abstract

The van der Waals interactions of acetylene with hydrogen-terminated diamond single crystal surfaces have been explored using infrared polarization spectroscopy at 83 K. By observing infrared spectra of the antisymmetric stretch of C 2 H 2 , the molecules are found to be adsorbed first on defect sites. This is followed by the adsorption on flat terraces that yields a single absorption at ν 0 ) 3225.6 cm -1 with a fwhm ) 5.4 cm -1 . The adsorbates lie nearly flat on the surface with a monolayer packing density of 5 × 10 14 molecules/ cm 2 and an adsorption energy of 23 kJ/mol. Isotope mixture experiments were also performed to provide information on the structure of the adsorbed phase. From the narrow width (fwhm < 3.0 cm -1 ) of the C 2 HD features and the result of exciton coupling calculations, it is suggested that the adsorbed layer forms a highly orientationally ordered superlattice. Two possible structures, (2×1) and (2×2) in ( 3× 3)R30°array, of the superlattice are proposed.

Breaking symmetry with hydrogen bonds: Vibrational predissociation and isomerization dynamics in HF–DF and DF–HF isotopomers

“…[2][3][4][5][6][7]28,29,[46][47][48][49][50] The highly nonstatistical nature of the predissociation event is reflected in the 30-fold decrease 4 in lifetime for HF-*HF vs *HF-HF as well as the bimodal j distribution of the HF fragments. 29 Furthermore, since even ''fast'' vibrational predissociation in these complexes occurs on a time scale of many hundreds of thousands of monomer vibrational periods, these represent exceedingly ''rare'' intermolecular energy transfer events, i.e., with very low probability per oscillation of the monomer.…”

“…The tunneling and K dependence is even more pronounced in the v HF ϭ2 manifold, which has been rationalized in terms of a dynamical coupling with the other members of the v HF ϭ2 triad. Chang and Klemperer 6,7 have observed all four members of the v HF ϭ3 tetrad of HF-HF, a system which demonstrates the highest mode selectiv-a͒ ity observed to date; specifically, the predissociation lifetimes for states with all three quanta in the bound vs free HF stretch differ by 100-fold. Recently, Anderson et al 8 have observed all four intermolecular vibrations in the v HF ϭ1 manifold of HF-HF, accessed as combination bands built upon either the free or bound HF stretch.…”

Determination of vibrational energy relaxation rates of C–H,D,T stretching modes on hydrogen, deuterium, and tritium-terminated H,D,T/C(111) and H,D,T/C(110) diamond surfaces using molecular dynamics simulation: Thermal effect

“…In addition, infrared ͑IR͒ spectroscopy was used to examine the vibrational dynamics of hydrogen, deuterium-covered diamond surfaces. 22,[25][26][27][28][29][30] From a peak width at the resonance frequency of 2120 cm Ϫ1 , a lifetime of 0.2 ps was found for C-D stretches on a D/C͑111͒ surface at room temperature. 22 A frequency of 2835.5 cm Ϫ1 at room temperature and small redshifts at high temperatures up to 1000 K were observed using IR spectroscopy.…”

Calculations of Vibrational Energy Relaxation Rates of C−H,D,T Stretching Modes on Hydrogen-, Deuterium-, and Tritium-Terminated H,D,T/C(111)1×1 Diamond Surfaces

“…Hydrogen on diamond surfaces has received a great deal of attention recently because of its role in chemical vapor deposition of diamond thin films. − The growth mechanism is substantially influenced by energy transfer between the vibrational modes on the surface and in the bulk. Many experiments have been carried out to probe the vibrational modes and the interactions between the adsorbates and surfaces on various surfaces. − Because of the development of the sum-frequency generation (SFG) spectroscopy, the vibrational modes on the surface can be resolved in the frequency domain as well as the time domain. On hydrogen-covered H/C(111) diamond surface, the C−H stretching mode was measured to be 2835.5 cm -1 using Infrared (IR) spectroscopy .…”